From the early days of the film industry, lighting has been an integral part of the movie making experience. Due to lack of sensitivity to light inherent in the types of film stock then used, artificial lighting was required in order to produce images on the screen that looked normal to the average human eye. The amount of light required for those early productions was excessive by today's standards, but was necessary in order to produce a realistic scene. Even today, the most technologically advanced, fully digital cameras, which are more sensitive to light than prior cameras, require some amount of light. Controlling this light is essential in order to produce images that reproduce well on theater screens, on televisions and on computer monitors. Each of the new, sophisticated movie digital cameras and still digital cameras respond to light and color in its own particular way. This is due to differences in which each camera manufacturer develops and adapts the photo sensors used in its cameras. Detailed information on the different types of and methods of configuring sensor arrays, and technical specifications for sensor arrays and technical specifications for commercially available cameras are publicly available.
As used herein, the term “luminaire” or “fixture” or “light source” refers to a complete light source, a light emitting device or a light fixture including control circuitry, if used. As is well known to those skilled in this field, the light output from commercially available luminaires varies in intensity and color, depending on the technology used, such as incandescent, fluorescent, high intensity discharge, etc. Even within the same technology variations from one luminaire to another are common. For example, variations in color and intensity of light are very noticeable even when comparing a new bulb to a same technology bulb made by the same manufacturer and that is at or near its end of life. As is well known to those skilled in this field, several fixtures from differing technologies are often used to illuminate a movie set and the talent, people and objects on the set. In recording any scene on the set, one typical goal is to have the light look as if it is emitted from an identical or similar source. In order to achieve this “similar source look” lighting technicians typically rely on conventional mechanical devices that assist in diminishing the luminance from a particular light source, or they modify the color emitted and as required for a particular shot. These devices include filters of various densities, gels of varying colors and densities, diffusion panels, scrims, intensifiers, and louvers. Also, many conventional lighting fixtures provide integrated focusing mechanisms that are used in combination with special lenses that allow “flood” and “spot” control of the light emitted from the fixture. “Flood” control produces a soft light that in turn produces soft shadows. “Spot” control focuses the emitted light into a narrow, tight, intense beam to highlight a particular section of the set.
Various other conventional methods of electronically dimming, that is lowering or raising the intensity of the light and rudimentary forms of color mixing are available to lighting technicians for trying to achieve the desired light intensity and color. However, conventional dimming is limited in use and is problematic in that it can produce undesired effects such as flicker and audible noise. Conventional color mixing, that is, rapid changes from one color to another color, is achieved by use of color wheels, gel color scrollers or cyc strips that are remotely controlled, usually via DMX or RDM protocol, as is well known to those skilled in this field. Also, in order to desaturate a color, a second, unfiltered unit, usually a white source, is placed next to the unit producing the color and is lowered or raised in intensity in order to produce the intended hue and/or degree of desaturation. This conventional solution in turn typically creates an intensity problem, and requires additional, typically by trial and error, efforts to achieve an acceptable intensity of the combined or mixed color. In the final stage of addressing these conventional problems is the problem of increasing or decreasing the intensity (ies) of the constituent colors in order to achieve the desired color at the desired intensity.
Color Mixing Problems Associated with Conventional LED-Based Lighting and Conventional, Adjustable Luminaire Settings
With the introduction of LED technology into this lighting field, more sophisticated controls for color and intensity have been developed. When used in combination with conventional means of light control mentioned previously, these sophisticated controls provide a more flexible and repeatable way of controlling the color and intensity of the light emitted from the source. New LED chips are continuously being developed, and these LED light sources typically provide higher lumen output while providing many, well-saturated color combinations and the ability to desaturate these colors as needed. However, known conventional methods for LED light control also have problems. These problems are essentially the same problems as found with conventional methods of color control described herein. When mixing, saturating or desaturating a specific color, the intensity of the light is typically either raised or lowered, and this light intensity change can potentially change the way the color is processed by the camera sensors, with variations on a camera-by-camera basis. As used herein the terms “light intensity” or “intensity” refers to the brightness of light emanating from a light source, and is measured in terms of “lumens”, with the term “lumen” defined to mean “a unit of luminous flux in the International System of Units, that is equal to the amount of light given out through a solid angle by a source of one candela intensity radiating in all directions.” As used herein the term “luminance” refers to and means candela per square meter (cd/m2). Luminance is a photometric measure of the luminous intensity per unit area of light traveling in a given direction, that is, the amount of light that passes through, is emitted or reflected from a particular area, and falls within a given solid angle. As is used herein the term “power” refers to the power that is input to a light source, measured in “watts” (“W”) and with the term “watt” defined to mean the amount of work done by a circuit in which one ampere of current is driven by one volt. As used herein the term “efficacy” means lumens per watt. Thus, as used herein the term intensity refers to the brightness of a light source, the term luminance refers to the intensity of light per unit area in a given direction, the term power refers to the electrical energy supplied to, or used by the light source to produce light and the term efficacy refers to the efficiency or capability of the light source to convert electrical energy into light. Also, as used herein the term “color” refers to and includes the concepts of “hue” or what is generally referred to as the color of something, the intensity, as referred to above, and the degree of “saturation” of a color, which means the degree or amount of white light that is mixed with some other color. For the purposes of the present systems and processes, a mixed white light, that is, a mixture of a relatively warm white and a relatively cool white light is preferably used. More specifically, as used herein white LED light is light that is produced by an LED that has one of several phosphor coatings, depending on the degree of warmness or coolness of the white desired.
Because of the wide variations in light sensors and in processing electronic signals corresponding to the light sensed from digital camera to digital camera, controlling the light sensed and then output from digital cameras presents additional problems in this field. More specifically, mixing colors including red, green, blue (RGB), amber (A), cool white and warm white represents specific problems for electronic shutter image capture devices, e.g., digital cameras. Different cameras from different manufacturers capture and process color differently from each other. These differences in color capturing and processing are considered to be significant differentiators between manufacturers and devices, and cause additional problems when cameras from different manufacturers are used on the same set.
To process color in a conventional digital camera, light is exposed to light-sensitive “pickups”, or sensors in the camera. The camera typically includes filters that separate full spectrum light into discrete red, green, and blue channels. Different designs for different cameras have different ratios of each red-, green-, and blue-filtered pickups in an attempt to create what each design considers the best or most desirable final image that is to be viewed by humans. Just as humans have “sensors” to perceive color and intensity in a particular way, so too do the various models of camera, varying from manufacturer to manufacturer. As a result there is variety in the color representations in the final image output from the cameras for the same input. In other words, for the same scene having the same lighting, different color will be output from different digital cameras. Because of these different color output differences that result from different design choices, no camera from one manufacturer will render a color representation image equal to the color representation image of any camera from another manufacturer, for the same object under the same lighting conditions. In other words the final image output will be different when different digital cameras are used to record the same scene under the same lighting conditions, regardless of the source(s) of the light.
In this field conventional RGB color mixing is typically performed by adjusting the intensity of each color using one of several electronic control methods commonly available. One such example is an LED-based RGB arrangement of LEDs, i.e., a light source using a conventional, 8-bit control, referred to as DMX, offering 256 discrete levels of intensity per color (including the absence of output or absence of power, which is the first level or “0” setting). One exemplary conventional system uses colors produced by one or more circuits supplying equal power to the LED(s), with each color in an individual circuit channel and each color controlled by an individual channel controller. In this example, when all three channels are operating at full power, the resulting blended color is a relatively low resolution variation of white based on the constituent wavelengths of light emitted from each of the colored LEDs, the power supplied to each LED and the relative efficacy of each LED. Even slight variations in wavelength of emitted light, power supplied to and/or efficacy of each LED can result in significantly different results in terms of intensity and/or color of light emitted from the light source(s). Because different cameras have different sensitivities to, and outputs for red, green and blue, respectively, each camera has the capability to capture and output any of 16,581,375 available, slightly different colors when using conventional 8-bit DMX protocol.
Another source of problems with color control for cameras, both digital and non-digital, relates to reproducing the color white. As is well known in this field, many different “white” lights are known, that is, many shades or variations of white are known, such as warm white and cool white. In this field the various white colors are associated with a specific Kelvin (K) temperature and typically referred to as correlated color temperature (CCT). As is also well known in this field, when producing an image from light reflected from an object, a photographer or cinematographer typically must choose a single CCT white to be used as a neutrally exposed, non-colored region of the desired image. As an example, choosing a 3200K film stock or selecting the same setting on an electronic shutter-based camera results in a perfect white, non-colored image when photographing a non-colored white object being illuminated with a 3200K light source. However, in the real world of photography and cinematography, particularly in this field, many different sources of “white” light are available and used. Many such sources of white light—both natural and artificial sources—would not appear “white” on a camera balanced for only a particular CCT, such as 3200K.
With respect to the color white problem or issue, at present, several different Kelvin temperature film stocks currently are commercially available and a wide range of white balance settings are available on conventional, electronic shutter-based cameras. Use of different film stocks and/or different camera settings are necessary if, for instance, the warm glow “white” from a sunset or a campfire is to appear colorless and white on camera while the same camera must also be able to render the cool “white” from an office fluorescent light to be colorless and white. A growing trend in image capture-intended luminaires is the integration of multicolor sources (such as RGB LEDs) within each luminaire and light from these sources is blended to produce a desired, white CCT. The blending typically is accomplished through use of conventional electronic control devices such as pulse width modulation (PWM) controllers or similar devices. The blended output of these multicolor luminaires can be adjusted for Kelvin temperature, hue, saturation and other parameters. In the present state of the color blending art these adjustments are made manually and relative only to the capabilities of the luminaire(s)—not to the camera—because, as is well known in this field, adjusting these parameters for a particular camera's color sensitivity is not intuitive.
Also, as is well known, in many specific lighting control situations, calibration of the camera(s) is needed or used. In a general, conventional lighting control instance, one level of hue, brightness and white balance control is provided by controlling the light output of the luminaires. Within this context, in some situations, the luminaire controls are set or fixed, but yet there is a need to further control or adjust one or more of hue, brightness, white balance, and such additional control can be achieved by controlling or calibrating aspects of the camera(s) used to record images. Conventional cameras can, and, in many instances must, be calibrated either in coordination with luminaire control or separately in order to achieve the desired color that is displayed on an output device, such as a monitor. Conventional camera calibration processes and techniques present additional challenges and problems in environments where color mixing, white balance control and saturation/desaturation are needed either in conjunction with luminaire control or independently of luminaire control. As is presently believed, in the conventional solution to the above-stated problems, for each “type” or “brand” of digital camera, calibration is accomplished manually and through trial and error efforts to compensate for the hue, brightness and white balance, based on the camera's known color sensitivity. The aspect of conventional color compensation though camera calibration is made on a per camera basis because of the differences in color sensitivity and processing among manufacturers and sensor types. The resulting, final image (after being processed by the camera) displays the color the photographer or cinematographer originally intended, which typically is the color as it would appear to the human eye under natural lighting conditions. An example of the importance of such color compensation or color rendering would be the capturing of a prominently featured red dress on the lead actress of a feature film. The subtleties of which shade of red or the consistency of the red color of the dress under different lighting conditions may have significant bearing on the success of the film. Capturing and uniform rendering of the color of the red dress, without color compensation and under different lighting conditions, such as day photography, night photography, the use of natural lighting, artificial lighting, or a mix of the two typically would create significant challenges because the final red color rendering of the dress would be different under each lighting condition.
White Light Problems Associated with Conventional Color Mixing Processes for LED Light Sources—and Compensated Color Mixing with Kelvin-Adjustable Desaturation Solutions
Conventional LED-based lighting systems and color mixing processes have several problems associated with color mixing and use of white light in color mixing. Four of these known problems that are addressed by the present systems and processes relate to problems associated with (i) brightness of colors that result from color mixing, (ii) quality of white light produced when color mixing is used to produce white light, (iii) mixing of different sources of white light and (iv) desaturating a non-white color light with white light.
Color Mixing Brightness Problem
Regarding conventional mixing of colors to yield a new color, such as mixing red and green to produce yellow, achieving accurate control of the brightness of the produced color is a problem that the conventional systems and processes have not been able to adequately solve. Consider, for example, mixing of primary red with primary green to yield yellow, to yield the correct brightness of the resulting yellow is an example of this problem. In conventional processes, the brightness of the resulting yellow color would be the sum of the brightness of the two constituent colors. In this example, the brightness of the red added to the brightness of the green used to create a particular shade or hue of yellow and could be as high as twice the brightness or double the brightness of the two mixed colors, such as when full power red is mixed with full power green. This conventional color mixing process in turn causes problems during filming or recording of specific scenes, due to varying brightness of differently mixed colors, and uneven capturing and reproducing colors on digital cameras and output media. For, example, a yellow produced by mixing of red at 100% of power with green at 100% of power could yield a yellow at twice the brightness of the constituent colors, but a different hue of yellow produced by mixing, for example, red at 100% with green at 50% power would yield a different hue of yellow and at a brightness of possibly 1.5 times the brightness of the red and three times the brightness of the green. This color mixing brightness problem occurs when mixing a non-white color with any shade of white color, and with mixing two or more shades of white with each other. The mixing of a pure non-white color with varying amounts of a white color is also referred to as “desaturation,” and is described in greater detail herein. This color brightness problem also occurs when mixing two or more different shades of white colors, as also described herein. In general, and in common for this type of problem, the conventional process simply adds one or more colors of light, each having its own intensity or brightness, to the chosen, base light, with its own intensity. The result of this typical mixing is that the brightness or intensity of the final, mixed color is the sum of the intensity (or brightness) of each component color and is greater than the individual intensity of any one of the component colors, regardless of whether the component colors are non-white and non-white; non-white and white; or white and white. The specific shade or Kelvin temperature of white used in any of these types of mixing introduces another set of problems, as also described herein.
Color Mixing to Produce White Light Problem
Regarding conventional production of white light from non-white colors of light, it is well known that tri-stimulus color mixing (RGB) provides a very broad range of blended final colors, including the mixing of colors to produce white light. However, as is well known in this field, when LED-sourced colors are mixed to create white light, a relatively low resolution and low quality white light results. Because high quality white light is made up of the entire visible spectrum, it is not possible to create high quality white light simply by blending only red, green, and blue light. Also, while it is known that the addition of light from another source, such as from a phosphor-white colored LED source, can help improve the quality of the final white light produced, this option is very limited in practice and is not capable of producing the highest quality of white light.
While the conventional solution to the color mixing to produce white light problem is use of multicolored light sources, and offers flexibility for adjusting the final output color white so that the final white light is within the human visible spectrum, this solution comes with a significant cost, i.e., relatively low quality of the white light produced. Also, while single, non-adjustable colored lights may be desired for some uses in which only a single, specific shade of white light is needed, the entertainment-based image capture field has historically desired and needed the ability to change the output parameters of lighting to meet ever-changing needs, including the need to produce various shades of high quality white light. This white light quality problem is believed to be solved with the presently disclosed systems and processes, as described in detail below.
From a photographic and cinematic point of view, artificial lighting is used to simulate the white produced by natural sources such as the sun, or fire, and white produced by other artificial light sources. As is well known in this field, natural white light from the sun from the point of view of a human standing on earth at midday or at sunset provide vastly different shades of white, and simulation of these vastly different shades of white presents significant challenges in the current state of the art. Because all or virtually all cameras used in this field, including film cameras, require the operator to choose the desired shade of white to appear “white” on camera during image capture, the differences between shades of white, and the ability to adjust for different shades of white under different conditions (such as early morning, midday or sunset, for example) is very important in this field. In the image capture market, the particular shade of white used by a camera is referred to as “white balance” and choosing and adjusting for differences in shades of white light requires the camera operator to choose a specific white balance, typically by choosing a specific setting on a camera, with the settings representing a wide range of shades of white. Such settings are typically found on cameras used in the cinematic, entertainment and photographic image capture field or markets.
Desaturation of a Non-White Color with White Light Problem
In current desaturation processes, otherwise unused portions of red, green, and blue light are typically employed to desaturate a chosen or predetermined base-color. As referred to herein, the terms “saturated” and “desaturated” mean and refer to the percentage of pure light of a predetermined, base color as compared to the percentage of light of the predetermined, base color after the base color has been mixed with white light regardless of the quality of the white light. Thus, for a predetermined, base color of light that is 100% pure of that predetermined color, that light is said to be saturated, fully saturated or 100% saturated. As a first example of saturation/desaturation, if the predetermined, base color is primary red and the light under consideration is 100% primary red, then that light is referred to as saturated, fully saturated or 100% saturated red. If a predetermined, base color of light, such as primary red, is mixed with white light such that 50% of the light is primary red and 50% is white light, then that light is referred to as 50% saturated red or 50% desaturated red. As a second saturation/desaturation example, if the predetermined, base color is primary blue and the mixed light has 40% primary blue light and 60% white light, the resulting color is referred to as either 60% desaturated blue, or 40% saturated blue light. As a third saturation/desaturation example, consider a predetermined, base color to be a shade of yellow. Yellow is the color resulting from mixing primary red and primary green, and a particular predetermined or base color that is a shade of yellow may be created from the many shades of yellow possible, depending on the percentage of red and green, respectively, used to create the base color yellow. Thus, for a particular base color of yellow, if that yellow was 75% desaturated, that yellow color would have 25% of the base shade of yellow light and 75% of white light, and could also be referred to as 25% saturated yellow.
The problematic effects of conventional color mixing are particularly noticeable when RGB is mixed for the purpose of producing white light and then using white light to desaturate a base color. One conventional process of producing desaturated light typically comprises using the unused portions of red, green, and/or blue to create white light and then using that white light to desaturate the chosen base color of light. A second, alternate conventional process of producing desaturated light is mixing RGB with an additional white LED-sourced light. As is known to those skilled in this field, this second desaturation technique does result in a better quality white than the first technique. However, the quality requirements for the cinema and television industries are very stringent for white light, and the goal of any artificial lighting system is accurate mimicking of natural light. While mixing RGB with or without an additional source of white light may be reasonable and acceptable for commercial or residential lighting, it is widely considered to be unacceptable for high-end applications such as for motion pictures, television, museums, etc.
As is well known to those skilled in this field, many variations of white light exist, with each hue of white associated with a specific Kelvin temperature (K). Also mixing of different Kelvin temperature white light is known in this field, and is commonly referred to as bi-color white mixing. One commercially available system and process of color mixing of white light has been available since 2010 from LiteGear, Inc., as its Hybrid™ brand white light. In one example of white light mixing, a 3000K (warm) white light could be mixed with a 6000K (cool) white light from two separate channels of LED emitted white light, resulting in a 4500K white light. This process of mixing could take place on a single printed circuit board, with two different channels of white light crossfaded to achieve the desired Kelvin temperature white light. In this example, the 3000K white light emitters would be powered from a first, single channel and start at, for example one watt of power (which could be defined or referred to as full power), and the 6000K white light emitters would be powered from a second, single channel and start at zero power output. During cross fading, as the power of the 3000K emitters is decreased, the power of the 6000K emitters is increased at the same rate, while the total output power would be maintained at one watt. In this example of white light mixing, the Kelvin temperature of the white light output changes from a relatively warm white to a relatively cool white, until the chosen or desired Kelvin temperature white is reached. However, use of such mixed or Hybrid™ white light has not been previously used to desaturate a fully saturated color, regardless of whether the fully saturated color is a primary color or a non-white, mixed color.
In sum and substance, several significant problems exist with conventional color mixing including varying of brightness during color adjustment, color mixing to produce white light, mixing of different hues of white and desaturating colored light. These problems associated with conventional color mixing processes in turn cause problems during filming of scenes, due to varying brightness, quality and hue of the mixed colors, and can and often do result in uneven capturing and reproducing of colors on digital cameras, and on output media.
As is readily apparent, needs exist to address the problems that currently exist with mixing of and controlling artificial light sources; and controlling color output from digital cameras as well as conventional film camera that record images illuminated by artificial light sources.